IF you look at the bottom of the air-box, it has a few vents to let water that gets into the air-box out....
Folks with CAI have been removing the plastic panel (separating the firewall/engine compartment), or cutting holes in for a long time (Swiss cheese Mod)....
IF you get the Dinian CAI it has a snorkel that get air from the opening at the base of the window...(or the JCW has a flap that opens...often locked open or removed), it has an additional hole to let more air in...same idea as cutting a larger hole in the firewall panel/back of the air box. Since the stock filter is so bad...a panel filter is a must if you mod the factory stock box....
That having been said...a CAI is pretty cheap...and will do more...but for a super cheap mod to get a bit more...from a stock car.....this might do a bit...

 

I just took a soldering iron and melted about 10-15 1/2" diameter holes in the cowl adjacent to the end of the K&N filter, seems to work great getting that extra air in the box, and took all of 5 minutes to do.

 

Lots of folks remove the entire panel...you can also buy them with the holes precut...kinda $$$, but simpler for some I guess who are afraid to rip it out.